Apparatus and process for continuous crystallization of sugar and the like



April 24, 1956 APPARATUS E. W. KOPKE I AND PROCESS FOR CONTINUOUS CRYSTALLIZATION OF SUGAR AND THE LIKE Filed Oct. 15, 1952 w ATTORNEYS:

APPARATUS AND PROCESS FOR CONTINUOUS I(JJIIgESTALLIZATION OF SUGAR AND THE Ernst W. Kopke, New York, N. -Y., assiguor to Ultra- Sucro Company, New York, N. Y a partnership of New York I Application October 15, 1952, Serial No. 314,871

. 21 Claims. (Cl. 127-15) This invention relates to crystallizers and more particularly to crystallizers used in the development of sugar crystals in massecuite. The massecuite resulting from certain operations in the hot into the sugar crystallizing apparatus; There, it is stirred While it is being cooled'and the sugar crystals are being developed. Many proposals, some of which have gone into commercial use, have been made for improving crystallizer performance and capacity. An object has always been to carry proper crystal development to a higher degree in the crystallizers while at the same time reducing as much as possible the time that the massecuite is in the crystallizers.

Heretofore, it has been common to treat massecuites in crystallizers by the batch method. A mass of material or batch of massecuite, derived from a preceding batch process such as in a vacuum pan, would be dumped into a crystallizer where it was cooled and stirred for as long period as the available capacity would permit. Frequently the crystallization would be for a shorter period than desirable, due to insufficient crystallizer capacity. From the crystallizer'the massecuite would then be discharged into a mixing tank supplying a subsequent process phase.

With this batch treatment, the more crystallizers that were used in a plant the larger would be the amount of material tied up in the process. Furthermore, while one batch was being treated in a crystallizer, others had to be stored and treated as accumulated; and additional crystallizers had to beprovided thus entailing increased investment in equipment.

One of the chief reasons for termination of crystallization in conventional practice is the fact that the massecuite becomes increasingly viscous as it cools. Therefore, despite the usual method and facilities for stirring, 'movement of the crystals in the mother liquor is retarded. During cooling and the slow stirring that characterizes usual practice, non-sugars or impurities adhere tenaciously to the crystal surfaces and counteract crystallization. Considerable of the non-sugars and impurities present in the final massecuite are insoluble, having been precipitated during preceding boiling phases and are of a very gummy nature. These impurities and non-sugars form a film over the crystals and obstruct its development I have found that when a sufliciently violent movement is imparted to the massecuite, the crystals undergo a rubbing effect which temporarily removes much of the adhering non-sugars and impurities and causes them to become mixed in with the surrounding mother liquor.

The more-exposed crystal surface after release from surface impurities can then proceed to develop more rapidly by taking on sucrose from the still unexhausted, saturated surrounding mother liquor. This final stage of development of sugar crystals is extremely slow.

Therefore it is an object of this invention to provide novel means to cause the vigorous movement necesmaking of sugar is dropped,

sary to expose the crystal surfaces for'further :develop ment.

Another object is to provide apparatus for use in I association with the above-mentioned novel apparatus which will accomplish relatively slow stirring along with longitudinal flow of the massecuite while it is being cooled.

Another object of the invention is to provide anapa paratus of the aforementioned typewhich will be subect to uniformity of crystal development through variation and control of the rate of stirring, cooling and vigorous motion or all three of those factors.

f Another object of the invention is to provide for more complete exhaustion of the sugar from the final massecuite and hence to make more economical the process of sugar crystallization. concomitantly, it isv an object to render the sugar crystallization more econorrlical by having less massecuite in process and thus to reduce the amount of space and crystallizing equipment necessary in the installation. 7 I

Another object is to provide a novel and improved apparatus and process for continuous and uninterrupted sugar crystallization from massecuite and other sugarbearing materials.

A further object is to embody in such apparatus and process a means to achieve the foregoing objectives.

Other objects and advantages will become apparent asthe invention is described in connection with the accompanyin g drawing.

In the drawing: I I

Fig. l is a plan view of a crystallizer installation embodying the principles and structure of my invention.

Fig. 2 is an elevational section view taken along line 22 of Fig. l with certain parts broken away for clarity.

In ordinary practice of the invention, three stages will be used each involving a crystallizer unit. However, the invention is not limited to use in that way but can be applied to a two-unit installation or even, though not preferably, to a single-unit. To avoid unnecessary repetition in illustration, the invention is depicted inthe drawing as applied to a two-unit installation. The two units are identical, the overflow from one feeding to the intake of the second. Hence in describing the installation, a single unit will be described. I

A deep, rectangular tank 4 having a semi-cylindrical bottom is mounted upona cradle 6 or other suitable supporting framework. Running along one side of the tank is a large round tube or pipe 8 which connects with the" side wall of the tank at one end to provide an outletl0 In the side wall of the from the tube into the tank. tank at the other end is a connection 12 with the tube 8 providing a re-entry port or inlet.

For supplying each crystallizer unit, a supply pipe Within the tube 8 and beneath the inlet 16 is a screw, conveyor or impeller 18 which is coaxial with the tubev and runs for at least a portion'of its length. In some circumstances, it may be desirable for the impeller to run the entire length of the tube but in the form illustrated the impeller extends into the tube for between /3 and /2 of its length. Forsupporting the impeller, a bearing and gland may be provided at one end of the tube. The bearing and gland structure per se forms no part of the invention. It will be understood however that the bearing should be of relatively heavy construction to stand the heavy duty imposed upon it by reason of the screw conveyor having to work upon the relatively viscous massecuite' and material familiar to workers inthe .art. The shaft of the screw conveyor may con- Patented Apr. 24, 1956 I veniently be driven from a reduction gear box 22 of conventional construction run by a motor 24.

The impeller 18 withdraws material continuously from the tank 4 and vigorously agitates and moves it along the tube causing rubbing of the crystals against one another and loosening the tenaciously adhering impurities from the surfaces of the crystals. The material is impelled through the tube 8 and re-enters the crystallizer tank 4 through the tube exit 10. The impeller 18 also continuously takes new material which is received through the inlet pipe 16. The new material is thus mixed in small quantities continuously with the material taken from the tank 4.

In this way, the material in the tank 4 is continuously recycled and mixed with new massecuite whereby the crystal growth is enhanced and a greater degree of crystallization can take place.

The relatively rapidly moving material issuing from the recycling tube moves into the much greater and more slowly moving mass in the crystallizer tank 4. In the tank, the mass is subjected repeatedly to cooling surfaces throughout its movement from one end to the other. At the same time, it is agitated and caused to move between the cooling surfaces and in such a manner as to avoid pockets of stagnant material.

To accomplish this movement and cooling within the crystallizer, I provide a shaft 30 concentric with the curvature of the bottom of the tank 4 mounted in bearings 32 in opposite end walls of the tank. For the purpose of causing rotation of the shaft 30, one end thereof extends beyond the tank wall and has mounted thereon a worm wheel 34 which meshes with a worm gear (not visible) on the shaft of a driving motor 36.

In order to disperse and move the material as it enters the end of the crystallizer tank 4 at the exit of the recycling tube 8, a pair of oppositely extending arms 40a are bolted or otherwise suitably secured to the shaft so as to extend in substantially radial directions. Mounted securely in any suitable fashion upon the arms a are stirring rods 42 which are spaced apart on the arms and extend parallel to the axis of the driver shaft 30 toward the end of the tank. By means of the arms 40a and the rods 42 the material entering the tank at the tube exit 10 is thoroughly dispersed and distributed over the whole area of the end of the crystallizer.

In order to cool the material as it moves along the tank, a number of cooling planes are provided in spaced relation along the length of the tank. The number of such planes will be determined by the length of the crystallizer and by the needs of particular installations. Five such planes are provided in the form illustrated, but it will be understood that the invention is not limited in that respect. Each cooling plane consists of pipe which is coiled or wound back and forth in a series of U-bends in a plane perpendicular to the axis of the shaft 30. Each of these sets of coils 43-48 inclusive is fed individually from a header pipe which conveniently is run parallel to and along the length of the tank. The flow of cooling water into the header may be controlled by a hand valve 52. Also, if desired, individual valves 53 may be provided in the pipes leading from the header to the individual coil sets. Preferably, the pipe of each coil set will initially go to the bottom portion of the tank and then wind back and forth upwardly of the tank to a point near the top thereof below the intended height of the material being processed. The upper end of the coil may be bent over the upper edge of the tank to discharge into a gutter 54 conveniently located alongside of the edge of the tank 4 opposite the header 50.

In order to continuously move the material out of the faster moving stream between the recycling tube exit 10 and re-entry port 12, and to distribute it over the whole transverse area of the tank as it flows along the length of the tank, and to agitate the material, a set of stirring arms such as 40b, 40c, 40d, 40c and 40 may be provided between the sets of coils 4348 and at the other end of the crystallizer tank. The arms 40 will preferably be located between the last set of cooling coils 48 and the end of the tank to avoid any possibility of a portion of the material in that zone becoming stagnant.

It will be apparent that the considerable force with which the impeller 18 causes the material to enter one end of the tank and the action of the impeller drawing in material from the other end of the tank will cause a constant and continuous movement of the material from one end of the tank to the other in the course of which movement the material will pass through the series of cooling coils or planes and will be constantly stirred between the various sets of cooling coils and hence cooled thoroughly and uniformly in a regulated and continuous fashion.

By reason of the fact that new material is constantly being fed into the crystallizer from the inlet 16, the processed material may constantly be withdrawn from the crystallizer by overflow through a trough 56, issuing from the top of the crystallizer at the side opposite the re-entry port, i. e. at the diagonally opposite upper corner from the tube exit 10. The material flowing along this overflow trough may be let into a second crystallizer unit through a connecting pipe 16'. This inlet and the second unit may be identical in structure and operation to the unit just described.

The frequency of recycling is such as to avoid readherence of a film of non-sugars and impurities on the crystal surfaces in suflicient amount to retard development during any phase of the process. The rearrangement for the recycling portions of the mass and then flowing it through the main crystallizer tank while being stirred is such that the overflow into the following unit represents a fair average of the material that has been subjected to many recyclings and treatments in the crystallizer tank.

The position of the overflow is important in that it prevents bypassing the treatment in any one unit of any portion of the material.

In this second unit, material which has already been processed will be processed to an even higher stage of crystal development and of exhaustion of sugar from the massecuite by being passed through cooling coils and vigorously recycled and redistributed through the recycling tube 8' in the same manner as in the first unit.

Finally the processed material from the second unit may be discharged through an outlet trough 56'. It may then be subjected in a third unit to further crystallization and cooling, or, if desired, to reheating since at that stage the material will have become very viscous and difficult to move.

Although I have illustrated in the drawings two units placed side by side and powered individually by separate motors for the impeller and for stirring the material in the crystallizing tank, the invention is not limited to such arrangement. If desired, the units may be placed in alignment with the impeller screw thrust being balanced by employing a right-hand screw in one unit and a lefthand screw in the adjacent unit on the same shaft. Insofar as the principle of the invention is concerned, it is immaterial whether the stirrers in the crystallizer tanks are separately driven or are driven from a single motor. From the foregoing, it will be observed that the apparatus which I have provided takes into account the fact that development of sugar crystals in the final stage of the usual sugar processing is slow due to the near-exhaustion of the sugar from the material and also to the presence of concentrated non-sugars and impurities. By providing vigorous action on a small portion of the material at a time, in the recycling tube, followed by slower stirring, mixing, cooling and crystallization in the large crystallizer tank, I retain the advantages of prior process procedures and improve their action, with the result that more sugar is crystallized out of the mass and less is lost in the residue. Moreover, all this is achieved in a continuous process, as distinguished from theusual batch processes.

' Many. modifications within the scope of my invention will occurto those skilled in the art. Therefore I do not limit the invention to the specific embodiment illustrated in the drawing. 4

What I claim is:

1. Apparatus for continuous crystallization of sugarbearing material comprising a tank, stirring means within the tank for stirring the material, heat transfer means in the tank for cooling or heating the material, conducting means adapted to continuously withdraw a small portion of the material from the mass circulating within the tank, means for vigorously agitating the Withdrawn portion to loosen impurities adhering to the crystal surfaces, said conducting means being adapted to return said portion directly to the mass circulating in the tank at a point remote from the withdrawal point, means to continuously introduce additional material into the tank, and means to continuously discharge treated material from the tank at a point removed from the point of introduction of the new material.

2. Apparatus as claimed in claim 1 in which the introducing means is adapted to introduce the additional material into said conducting means in position to be subjected to the action of said agitating means.

3. Apparatus as claimed in claim 1 wherein said introducing means is adapted to introduce said additional material adjacent the inletto said agitating mechanism andto cause it to enter into said agitating mechanism.

4. Apparatus for continuous crystallization of sugarbearing material comprising a tank, stirring means within the tank for stirring the material, heat transfer means in the tank for cooling or heating the material, a tube connected to opposite ends of said tank, impeller means in said tube causing withdrawal of a portion of the ma terial from one end of the tank and vigorous agitation and movement through the tube and return of said portion to the tank, means to continuously introduce additional material into the tank adjacent the-inlet of said agitating mechanism and to cause it thereupon to enter into said agitating mechanism, and means to continuously discharge treated material from the tank at a point removed from the point of introduction of the new material.

5. Apparatus as claimed in claim 4 having means moving in said tank in the zone adjacent the re-entrance of said agitated portion and having elements extending therefrom adapted to distribute that portion through the mass of material in the tank.

6. Apparatus as claimed in claim 5 in which the heat transfer means comprises pipe coiled in planes spaced along the tank, and the stirring means moves between adjacent heat transfer planes to cause movement of the material between said planes.

7. Apparatus as claimed in claim 1 in which the heat transfer means comprises pipe coiled in planes spaced along the tank, and the stirring means moves between adjacent heat transfer planes to cause movement of the material between said planes.

8. Apparatus as claimed in claim 1 having means moving in said tank in the zone adjacent the re-entrance of said agitated portion and having elements extending therefrom adapted to distribute that portion through the mass of material in the tank.

9. Apparatus as claimed in claim 8 havingmeans oppositely placed along the tank for discharging material which has been treated as additional material enters the tank.

10. Apparatus as claimed in claim 4 in which the heat transfer means comprises pipe coiled in planes spaced along the tank, and the stirring means moves between adjacent heat transfer planes to cause movement of the material between said planes.

11. Apparatus for continuous crystallization of sugaring-means adapted to continuouslywithdraw a small portion-of the material from the mass circulating within the; tank, means for vigorously agitating the withdrawn por-- tion to loosen impurities adhering to the crystal surfaces, said conducting means being adapted to return said portion directly to the mass circulating in the tank at a point remote from the withdrawal-point. I j';

12. Apparatus for continuous crystallization. of sugarbearing material comprising a tank, stirring means within the tank for stirring the material, heat transfer means in the tank for cooling or heating the material, a tube connected to opposite ends of said tank, impeller means in said tube adapted to withdraw a portion of the material from one end of the tank and to vigorously agitate it and to move it through the tube and to return it to the tank.

13. Apparatus as claimed in claim 12 in which the impeller means is a screw conveyer.

14. Apparatus as claimed in claim 12 having means moving in said tank adjacent the tube exit and having elements extending therefrom adapted to distribute the material issuing from the tube through the mass of material in the tank. 15. Apparatus as claimed in claim 14 in which the heat transfer means comprises pipe coiled in planes spaced along the tank, and the stirring means moves between adjacent heat transfer planes to cause movement of the material between said planes.

16. Apparatus as claimed in claim 11 having means moving in said tank in the zone adjacent the re-entrance of said agitated portion and having elements extending therefrom adapted to distribute that portion through the mass of material in the tank.

17. Apparatus as claimed in claim 11 in which the heat transfer means comprises pipe coiled in planes spaced along the tank, and the stirring means moves between adjacent heat transfer planes to cause movement of the material between said planes.

18. Apparatus as claimed in claim 11 having means placed along the tank oppositely to entering material for discharging material which has been treated as additional material enters the tank.

19. The process of crystallization of sugar from sugarbearing material, comprising continuously stirring and cooling a large mass of material to form sugar crystal, continuously withdrawing a small portion of the material from said mass at one point, agitating said withdrawn portion with a more vigorous action than said stirring action to cause loosening of the adhering film from the crystal surfaces, returning said withdrawn portion directly to said mass at a point remote from said withdrawal point. i

20. The process of crystallization of sugar from sugarbearing material, comprising continuously stirring and cooling a large mass of material to form sugar crystals, continuously withdrawing a small portion of the material from said mass at one point, agitating said withdrawn portion with a more vigorous action than said stirring action to cause loosening of the adhering film from the crystal surfaces, returning said withdrawn portion directly to said mass at a point remote from said withdrawal point, continuously adding new material to said mass, and continuously discharging treated material from the mass at a point removed from both said withdrawal and return points.

21. The process of crystallization of sugar from sugarbearing material, comprising continuously stirring and cooling a large mass of material to form sugar crystals, continuously withdrawing a small portion of the material from said mass at one point, agitating said withdrawn portion with a more vigorous action than said stirring action to cause loosening of the adhering film from the crystal surfaces, returning said withdrawn portion directly to said mass at a point remote from said withdrawal point, continuously adding and mixing new material to said withdrawn portion and thereby introducing new material to said mass, and continuously discharging treated material from the mass at a point removed from said return point.

989,366 Kestner Apr. 11, 1911 8 Kopke Mar. 4, 1930 Widmer Feb. 25, 1936 Copland Oct. 29, 1940 Buck et al. Apr. 29, 1952 FOREIGN PATENTS Great Britain June 22, 1945 

1. APPARATUS FOR CONTINUOUS CRYSTALLIZATION OF SUGARBEARING MATERIAL COMPRISING A TANK, STIRRING MEANS WITHIN THE TANK FOR STIRRING THE MATERIAL, HEAT TRANSFER MEANS IN THE TANK FOR COOLING OR HEATING THE MATERIAL, CONDUCTING MEANS ADAPTED TO CONTINUOUSLY WITHDRAW A SMALL PORTION OF THE MATERIAL FROM THE MASS CIRCULATING WITHIN THE TANK, MEANS FOR VIGOROUSLY AGITATING THE WITHDRAWN PORTION TO LOOSEN IMPURITIES ADHERING TO THE CRYSTAL SURFACES, SAID CONDUCTING MEANS BEING ADAPTED TO RETURN SAID PORTION DIRECTLY TO MASS CIRCULATING IN THE TANK AT A POINT REMOTE FROM THE WITHDRAWAL POINT, MEANS TO CONTINUOUSLY INTRODUCE ADDTIONAL MATERIAL INTO THE TANK, AND MEANS TO CONTINUOUSLY DISCHARGE TREATED MATERAIL FROM THE TANK AT A POINT REMOVED FROM THE POINT OF INTRODUCTION OF THE NEW MATERIAL. 